Existing homeowners don't usually oppose new development in order to maximize their property values. They are usually more motivated by quality of life issues. Some people specifically chose to live in low-density suburbs in order to have a little space, privacy, and quiet. It's hard to convince them to put up with more noise and traffic congestion just so that newcomers can have cheaper housing.

What percentage of home owners are people who have owned their house for a long time (to benefit from prop 13), need zero work done (unlikely if you've owned your house for a long time), and whose behavior can be reduced to a financial equation?

My guess is that a lot of people do interior work without permits. If you're tearing down an interior wall and re-building a bathroom, there's no evidence of that from outside, so no simple way for the city to stop you.

There is tons of this in SF, notably the huge number of illegally built "in-law apartments," where someone converts their garage or basement into a seperate dwelling unit without permits.

Hell if I know. Look it up and post it here if you're that interested. I have things to do.